Adenosine is commonly used for the chemical termination of supraventricular tachycardia. In addition, even when it is ineffective as an agent of chemical cardioversion, it may slow the cardiac rate to allow an analysis of the underlying rhythm. Common adverse effects include facial flushing, shortness of breath, and chest pain. Major contraindications include heart blocks and known adenosine hypersensitivity. This case report illustrates an episode of cardiopulmonary arrest after adenosine administration and, to the authors' knowledge, is the first occurrence reported in the literature.